Nitrogen containing steels with high creep resistance and high tensile strength at elevated temperatures



Patented July 15, 1952 NI'IROGEN CONTAINING STEELS WITH I HIGH CREEP RESISTANCE AND men. TENSILE STRENGTH AT ELEvA'rEn,

'. a TEMPERATURES Franz' Rapatz, Kapfenberg, Austria, assignor to Gebr. Biihler & Co. Aktiengesellschaft,

Austria No Drawing. rial vNo.

Section 1, Pub

Vienna,

Application February 27, 1948, Se-

l1,857. In Germany November 27,

lic Law 600, August 8, 1946 Patent expires November 2'}, 1963 2 Claims. (01. 75-423) The present invention relates to steels with high creep resistance and high tensile strength at elevated temperatures containing nitrogen not combined with iron, chromium or manganese, but with metals which form nitrides of low solubility in steel such as elements of the 3rd group of the periodic system such as aluminium, the 4th group such as titanium and zirconium or the 5th group such as columbium. The effect of nitrogen already existing is increased to a. surprising degree by the formation of stable nitrides of low solubility.

This increased effect is indicated by the following experimental results:

Composition of the steels zirconium or the 5th group as columbium are subsequently added to the steel already con- Similar values are also obtained when only elements or the 2nd group e. g. titaniumor zirconium-combined nitrogen are present. It is therefore apparent that presence of nitrogen alone is not sumcient, but what matters is the manner in which it is combined. In the case of steels as quoted in 2 and 3, values of creep resistance are obtained as' are otherwise only obtained with relatively high additions of alloying metals (see Die Edelstahle by Dr. Rapatz, published by Springer, Berlin, 3rd edition, 1942, p. 145). According to the present invention the amount of alloying elements is very low-an important factor in view of the scarcity of such raw materials. What other metals may he used is a matter of the experimental technique applied. The quantity of insoluble nitride formed in the steel must not exceed 0.03%.

The strengthening effect of nitrogen seems to depend also on its state of distribution the latter being already controlled by the conditions prevailing in the heat. This favorable degree of distribution is reached, for example, if the nitrogen is first introduced into the steel in the form of nitrides of iron or chromium, and then elements of the 3rd group of the periodic system such as aluminium, the 4th group such as titanium and periodic system such as aluminium, the 4th group as titanium and zirconium or the 5th group such as columbium which form nitrides of low solubility are present in the core wire or in the coating of the welding rod. In order to increase the creep resistance or tensile strength at elevated temperatures or for obtaining other efiects, steels may be used which usually are alloyed with chromium, manganese, molybdenum, tungsten or nickel. v

Theinvention is similarly applicable to structural steels having high creep resistance and also to tool steels which require creep resistance or high tensile strength at elevated temperatures, for example high grade steels intended for work at elevated temperatures and high speed steels.

I claim:

1. A steel having a high tensile strength, wear resistance and creep resistance containing a small quantity, not exceeding .03%, of the steel of a nitride selected from the group consisting of aluminum, titanium, zirconium and columbium homogeneously distributed throughout the steel, said steel being produced by first dissolving in the molten steel a nitride of at least one metal selected' from the group consisting of iron and chromium in amounts suflicient to leave at least 3 .07% nitrogen in the thereof, then adding tosaid molten steel solution containing *said :metal .nitride a :metal, selected from thesgroup consisting of aluminum, titanium, zirconium and columbium to convert a portion of the nitrides therein to nitrides of insoluble form homogeneously distributed throughout steel.

The following references are nflrecord .in the file of this patent: V V UNITED STATES PATENTS .Name Q j Date Number Russel 'Nov. 14', 1920 steel upon solidification the 2,. A wemea steel product ihating its joints f Number Name Date 2,022,307 Austin Nov. 26, 1935 2,040,189 Strauss -1- :May 12, 1935 2,121,055 vSmith etr.a;l-.l June 21, 1938 2,121,056 Smith et a]. June 21, 1938 2,174,740 Graham et a1 Oct. 3, 1939 2,229,140 Smith et a1. Jan. 21, 1941 1;; 2,370,289 Chandler Feb. 27, 1945 FOREIGN PATENTS Number Country Date 195,385 Switzerland Apr. 16, 1938 OTHER REFERENCES Mining and Metallurgical Investigations, Co- Operative Bulletin 66, pages 19 and 20. Edited by Herty, Jr., etal. Published by the Mining and Metallurgical Boards, Pittsburgh, Pennsylvania. 

1. A STEEL HAVING A HIGH TENSILE STRENGTH, WEAR RESISTANCE AND CREEP RESISTANCE CONTAINNG A SMALL QUANTITY, NOT EXCEEDING .03%, OF THE STEEL OF A NITRIDE SELECTED FROM THE GROUP CONSISTING OF ALUMINUM, TITANIUM, ZIRCONIUM AND COLUMBIUM HOMOGENEOUSLY DISTRIBUTED THROUGHOUT THE STEEL, SAID STELL BEING PRODUCED BY FIRST DISSOLVING IN THE MOLTEN STEEL A NITRIDE OF AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF IRON AND CHROMIUM IN AMOUNTS SUFFICIENT TO LEAVE AT LEAST .07% NITROGEN IN THE STEEL UPON SOLIDIFICATION THEREOF, THEN ADDING TO SAID MOLTEN STEEL SOLUTION CONTAINING SAID METAL NITRIDE A METAL SELECTED FROM THE GROUP CONSISTING OF ALUMINUM, TITANIUM, ZIRCONIUM AND COLUMBIUM TO CONVERT A PORTION OF THE NITRIDES THEREIN TO NITRIDES OF INSOLUBLE FROM HOMOGENEOUSLY DISTRIBUTED THROUGHOUT THE STEEL. 